Toothed endless power transmission belts made primarily of elastomeric material have been proposed previously and are in wide use throughout industry and each of such toothed belts usually has improved flexibility while having better transverse rigidity than on untoothed belt.
It has also been proposed previously to provide a roughly trapezoidal endless power transmission belt with an upwardly convex top surface and load-carrying section in an effort to improve its transverse rigidity.
However, previously proposed belts including the above-mentioned belts are deficient because they do not provide both an optimum flexibility and transverse rigidity inasmuch as such belts when made to be more flexible will usually tend to dish when operated in sheaves under comparatively high load.